Method and Apparatus for Image-Based Navigation

ABSTRACT

A system and method for a procedure that can be performed on any appropriate subject. Procedures can include assembling any appropriate work piece or installing members into a work piece, such as an airframe, autoframe, etc. Regardless of the subject, tracking a substantially small tracking device in a plurality of degrees of freedom is provided. The tracking device can be positioned on or be formed in an instrument to be tracked.

FIELD

The present disclosure is related to surgical procedures, andparticularly to surgical procedures that are navigated or use computerassisted surgery for performing a surgical procedure.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

A procedure can be performed on any appropriate subject. For example, aprocedure can be performed on a patient to position an implant in thepatient. Though procedures can also include assembling any appropriatework piece or installing members into a work piece, such as an airframe,autoframe, etc. Regardless of the subject, generally the procedure canhave a selected result that is efficacious. The efficacious result maybe the desired or best result for the procedure.

A procedure on a human patient can be a surgical procedure performed toinsert an implant, such as a pedicle screw. The pedicle screw can beplaced in the patient according to appropriate techniques, such as anopen procedure where a surgeon can view the procedure. Also, procedurescan include hole drilling, screw placement, vessel stent placement, deepbrain stimulation, etc.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A surgical procedure can be performed with a navigated instrument. Thenavigated instrument can have associated therewith, such as attacheddirectly to or relative to a surgical instrument, a tracking device totrack a location of the instrument. The tracking device can beinterconnected directly, such as wrapped around or positioned around aportion of an instrument, or extend from a mounting device connected tothe instrument. According to various embodiments, a surgical procedurecan be performed using a small or low invasive instrument. A small orlow invasive instrument, however, may require or benefit from a smalltracking device associated with an instrument for tracking a location ofthe instrument while minimizing a space or volume consumed by thetracking device itself. Accordingly a tracking device can be providedthat is wrapped around an axis of an instrument, embedded in a surfaceof an instrument, or positioned or embedded in an interior of aninstrument to minimize a dimensional increase due to the inclusion of atracking device. Such instruments may also be used for air frameassembly or small (e.g. robotic) system repair.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is an environmental view of an operating theatre including anoptional imaging system and a navigation system;

FIG. 2 is a perspective view of a tracking device on an instrument,according to various embodiments;

FIG. 3 is a detail perspective view of the tracking device of FIG. 2 onan instrument, according to various embodiments;

FIG. 4 is a plan view of a tracking device on an instrument, accordingto various embodiments;

FIG. 5A is a plan view of a tracking device on an instrument, accordingto various embodiments;

FIG. 5B is an end plan view the tracking device on an instrumentillustrated in FIG. 5A;

FIG. 6 is a perspective view of a tracking device on an instrument,according to various embodiments;

FIG. 7 is a perspective view of a tracking device on an instrument,according to various embodiments;

FIG. 8 is a detail perspective view of the tracking device of FIG. 7 onan instrument, according to various embodiments; and

FIG. 9 is a plan view of an instrument with a tracking device, accordingto various embodiments.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings. According to various embodiments, a trackingdevice can be attached or interconnected with various portions in anavigation system. For example, a tracking device can be wrapped aroundor integrated into a portion of an instrument, such as in a shaft of astylet or on a shaft of a stylet. Alternatively, or in addition thereto,a tracking device can be formed separately and connected, such as with aconnection member with an instrument to be tracked. Accordingly, aninstrument can include a tracking device that is wrapped directly aroundor placed directly on a portion of the instrument or it can beseparately interconnected with a portion of the instrument. For example,the tracking device can be clipped or passed over a portion of theinstrument.

FIG. 1 is a diagram illustrating an overview of a navigation system 10that can be used for various procedures. The navigation system 10 can beused to track the location of an item, such as an implant or aninstrument (e.g. 100 as discussed herein), relative to a subject, suchas a patient 14. It should further be noted that the navigation system10 may be used to navigate any type of instrument, implant, or deliverysystem, including: guide wires, arthroscopic systems, orthopedicimplants, spinal implants, deep brain stimulation (DBS) probes, etc.Non-human or surgical procedures may also use the instrument 100 and thenavigation system 10. Moreover, the instruments may be used to navigateor map any region of the body. The navigation system 10 and the varioustracked items may be used in any appropriate procedure, such as one thatis generally minimally invasive or an open procedure.

The navigation system 10 can interface with or integrally include animaging system 12 that is used to acquire pre-operative,intra-operative, or post-operative, or real-time image data of thepatient 14. It will be understood, however, that any appropriate subjectcan be imaged and any appropriate procedure may be performed relative tothe subject. In the example shown, the imaging system 12 comprises anO-arm® imaging device sold by Medtronic Navigation, Inc. having a placeof business in Louisville, Colorado, USA. The imaging device 12 includesimaging portions such as a generally annular gantry housing 20 thatencloses an image capturing portion 22. The image capturing portion 22may include an x-ray source or emission portion 26 and an x-rayreceiving or image receiving portion 28. The emission portion 26 and theimage receiving portion 28 are generally spaced about 180 degrees fromeach other and mounted on a rotor (not illustrated) relative to a trackof the image capturing portion 22. The image capturing portion 22 can beoperable to rotate 360 degrees during image acquisition. The imagecapturing portion 22 may rotate around a central point or axis, allowingimage data of the patient 14 to be acquired from multiple directions orin multiple planes.

The imaging system 12 can include those disclosed in U.S. Pat. Nos.7,188,998; 7,108,421; 7,106,825; 7,001,045; and 6,940,941; all of whichare incorporated herein by reference. The imaging system 12 can alsoinclude or be associated with various image processing systems, asdiscussed herein. Other possible imaging systems can include C-armfluoroscopic imaging systems which can also be used to generatethree-dimensional views of the patient 14. It is also understood thatother appropriate imaging systems can be used such as magnetic resonanceimaging (MRI), positron emission tomography imaging (PET), etc.

The patient 14 can be fixed onto an operating table 29, but is notrequired to be fixed to the table 29. The table 29 can include aplurality of straps 29 s. The straps 29 s can be secured around thepatient 14 to fix the patient 14 relative to the table 29. Variousapparatuses may be used to position the patient 14 in a static positionon the operating table 29. Examples of such patient positioning devicesare set forth in commonly assigned U.S. patent application Ser. No.10/405,068, published as U.S. Pat. App. Pub. No. 2004-0199072 on Oct. 7,2004, entitled “An Integrated Electromagnetic Navigation And PatientPositioning Device”, filed Apr. 1, 2003 which is hereby incorporated byreference. Other known apparatuses may include a Mayfield® clamp.

The navigation system 10 includes a tracking system 30 that can be usedto track instruments relative to the patient 14 or within a navigationspace. The navigation system 10 can use image data from the imagingsystem 12 and information from the tracking system 30 to illustratelocations of the tracked instruments, as discussed herein. The trackingsystem 30 can include a plurality of types of tracking systems includingan optical tracking system that includes an optical localizer 40 and/oran electromagnetic (EM) tracking system that can include an EM localizer42 that communicates with or through an EM controller 44. The opticaltracking system 40 and the EM tracking system with the EM localizer 42can be used together to track multiple instruments or used together toredundantly track the same instrument. Various tracking devices,including those discussed further herein, can be tracked with thetracking system 30 and the information can be used by the navigationsystem 10 to allow for an output system to output, such as a displaydevice to display, a position of an item. Briefly, tracking devices,such as a patient tracking device (to track the patient 14) 48, animaging device tracking device 50 (to track the imaging device 12), andan instrument tracking device 52 (to track the instrument 100), allowselected portions of the operating theater to be tracked relative to oneanother with the appropriate tracking system, including the opticallocalizer 40 and/or the EM localizer 42.

It will be understood that any of the tracking devices 48-52 can beoptical or EM tracking devices, or both, depending upon the trackinglocalizer used to track the respective tracking devices. It will befurther understood that any appropriate tracking system can be used withthe navigation system 10. Alterative tracking systems can include radartracking systems, acoustic tracking systems, ultrasound trackingsystems, and the like.

An exemplarily EM tracking system can include the STEALTHSTATION® AXIEM™Navigation System, sold by Medtronic Navigation, Inc. having a place ofbusiness in Louisville, Colo. Exemplary tracking systems are alsodisclosed in U.S. Pat. No. 7,751,865, issued Jul. 6, 2010 and entitled“METHOD AND APPARATUS FOR SURGICAL NAVIGATION”; U.S. Pat. No. 5,913,820,titled “Position Location System,” issued Jun. 22, 1999 and U.S. Pat.No. 5,592,939, titled “Method and System for Navigating a CatheterProbe,” issued Jan. 14, 1997, all herein incorporated by reference.

Further, for EM tracking systems it may be necessary to provideshielding or distortion compensation systems to shield or compensate fordistortions in the EM field generated by the EM localizer 42. Exemplaryshielding systems include those in U.S. Pat. No. 7,797,032, issued onSep. 14, 2010 and U.S. Pat. No. 6,747,539, issued on Jun. 8, 2004;distortion compensation systems can include those disclosed in U.S. Pat.No. 10/649,214, filed on Jan. 9, 2004, published as U.S. Pat. App. Pub.No. 2004/0116803, all of which are incorporated herein by reference.

With an EM tracking system, the localizer 42 and the various trackingdevices can communicate through the EM controller 44. The EM controller44 can include various amplifiers, filters, electrical isolation, andother systems. The EM controller 44 can also control the coils of thelocalizer 42 to either emit or receive an EM field for tracking. Awireless communications channel, however, such as that disclosed in U.S.Pat. No. 6,474,341, entitled “Surgical Communication Power System,”issued Nov. 5, 2002, herein incorporated by reference, can be used asopposed to being coupled directly to the EM controller 44.

It will be understood that the tracking system may also be or includeany appropriate tracking system, including a STEALTHSTATION® TRIA®,TREON®, and/or S7™ Navigation System having an optical localizer,similar to the optical localizer 40, sold by Medtronic Navigation, Inc.having a place of business in Louisville, Colo. Further alternativetracking systems are disclosed in U.S. Pat. No. 5,983,126, to Wittkampfet al. titled “Catheter Location System and Method,” issued Nov. 9,1999, which is hereby incorporated by reference. Other tracking systemsinclude an acoustic, radiation, radar, etc. tracking or navigationsystems.

The imaging system 12 can further include a support housing or cart 56that can house a separate image processing unit 58. The cart can beconnected to the gantry 20. The navigation system 10 can include anavigation processing unit 60 that can communicate or include anavigation memory 62. The navigation processing unit 60 can include aprocessor (e.g. a computer processor) that executes instructions todetermine locations of the tracking devices 48-52 based or signals fromthe tracking devices. The navigation processing unit 60 can receiveinformation, including image data, from the imaging system 12 andtracking information from the tracking systems 30, including therespective tracking devices 48-52 and the localizers 40-42. Image datacan be displayed as an image 64 on a display device 66 of a workstationor other computer system 68 (e.g. laptop, desktop, tablet computer whichmay have a central processor to act as the navigation processing unit 60by executing instructions). The workstation 68 can include appropriateinput devices, such as a keyboard 70. It will be understood that otherappropriate input devices can be included, such as a mouse, a foot pedalor the like which can be used separately or in combination. Also, all ofthe disclosed processing units or systems can be a single processor(e.g. a single central processing chip) that can execute differentinstructions to perform different tasks.

The image processing unit 58 processes image data from the imagingsystem 12 and transmits it to the navigation processor 60. It will befurther understood, however, that the imaging system 12 need not performany image processing and it can transmit the image data directly to thenavigation processing unit 60. Accordingly, the navigation system 10 mayinclude or operate with a single or multiple processing centers or unitsthat can access single or multiple memory systems based upon systemdesign.

In various embodiments, the imaging system 12 can generate image datathat can be registered to the patient space or navigation space. Invarious embodiments, the position of the patient 14 relative to theimaging system 12 can be determined by the navigation system 10 with thepatient tracking device 48 and the imaging system tracking device 50 toassist in registration. Accordingly, the position of the patient 14relative to the imaging system 12 can be determined.

Alternatively, or in addition to tracking the imaging system 12, theimaging system 12, such as the O-arm® imaging system, can know itsposition and be repositioned to the same position within about 10microns. This allows for a substantially precise placement of theimaging system 12 and precise determination of the position of theimaging device 12. Precise positioning of the imaging portion 22 isfurther described in U.S. Patent Nos. 7,188,998; 7,108,421; 7,106,825;7,001,045; and 6,940,941; all of which are incorporated herein byreference.

Subject or patient space and image space can be registered byidentifying matching points or fiducial points in the patient space andrelated or identical points in the image space. When the position of theimaging device 12 is known, either through tracking or its “known”position (e.g. O-arm® imaging device sold by Medtronic, Inc.), or both,the image data is generated at a precise and known position. This canallow image data that is automatically or “inherently registered” to thepatient 14 upon acquisition of the image data. Essentially, the positionof the patient 14 is known precisely relative to the imaging system 12due to the accurate positioning of the imaging system 12. This allowspoints in the image data to be known relative to points of the patient14 because of the known precise location of the imaging system 12.

Alternatively, manual or automatic registration can occur by matchingfiducial points in image data with fiducial points on the patient 14.Registration of image space to patient space allows for the generationof a translation map between the patient space and the image space.According to various embodiments, registration can occur by determiningpoints that are substantially identical in the image space and thepatient space. The identical points can include anatomical fiducialpoints or implanted fiducial points. Exemplary registration techniquesare disclosed in Ser. No. 12/400,273, filed on Mar. 9, 2009,incorporated herein by reference.

Once registered, the navigation system 10 with or including the imagingsystem 12, can be used to perform selected procedures. Selectedprocedures can use the image data generated or acquired with the imagingsystem 12. Further, the imaging system 12 can be used to acquire imagedata at different times relative to a procedure. As discussed herein,image data can be acquired of the patient 14 subsequent to a selectedportion of a procedure for various purposes, including confirmation ofthe portion of the procedure.

With continuing reference to FIG. 1, the imaging system 12 can generateactual three dimensional images of the patient 14 or virtual threedimensional images based on the image data, which can be registered tothe patient/navigation space. The patient 14 can be placed relative tothe imaging system 12 to allow the imaging system 12 to obtain imagedata of the patient 14. To generate 3D image data, the image data can beacquired from a plurality of views or positions relative to the patient14. The 3D image data of the patient 14 can be used alone or with otherinformation to assist in performing a procedure on the patient 14 or anappropriate subject. It will be understood, however, that anyappropriate imaging system can be used, including magnetic resonanceimaging, computed tomography, fluoroscopy, etc.

As generally illustrated in FIG. 1, the navigation system 10 can be usedto navigate the instrument 100 relative to the patient 14. Thenavigation can be imageless (e.g. only illustrating icons at trackedlocations of different tracked portions) or with images. Images caninclude acquired images (e.g. with the imaging system 12 or atlasimages). Regardless, icons with or without images can be displayed onthe display device 66. The tracking system 30 can track the instrument100 and the navigation processing unit 60 can be used to determine thelocation of the instrument 100 and display the location of theinstrument on the display 66 relative to the image 64 or, as mentionedabove, without the image 64. Accordingly, according to variousembodiments, such as those discussed herein, the user 54 can view anicon representing a location of the instrument 100 relative to thepatient 14 or a selected portion of the patient 14 with or withoutimages on the display 66. In so viewing the icons the user 54 can knowthe location of the instrument 100 in subject/patient space based uponthe tracked location of the instrument 100 in image space.

The tracking device 52 can include various features, such as thosediscussed herein. In an EM tracking system 30 the tracking device 52 caninclude one or more coils that can either transmit an EM field or sensean EM field to generate a tracking signal (also referred to as an EMsignal) to allow the navigation system 10 to determine the location ofthe tracked instrument 100 in the navigation space. The coils of thetracking device 52 can be formed as a wire wrapped around a core (e.g.formed of a solid material or air) or axis that can sense the magneticfield by generating a current within the wire or transmit an EM fieldthat can be sensed by a sensing or localizer coil. The tracking device52 can be formed directly on a device, as illustrated below, or,according to various embodiments, be connected to the instrument 100 tobe tracked, as illustrated in FIG. 1.

As discussed above in relation to FIG. 1, the navigation system 10 caninclude the various localizers 40, 42 relative to respective trackingdevices 52 associated with the instrument 100, which can be a guidetube. The instrument 100, as illustrated in FIGS. 2-3, can be anyappropriate instrument as exemplarily illustrated as a guide tubeincluding a cannula or bore 102 extending along a length of the guidetube 100. It will be understood, however, that the instrument 100 canalso include or be formed as a drill bit, a probe, or any otherappropriate instrument. Additionally, the guide tube 100 can besubstantially solid or itself designed as the tracking device 52 thatcan be associated with other instruments to be navigated with thenavigation system 100.

The tracking device 52 is formed as a plurality of winds of wire 110formed around an exterior or on an exterior wall 112 of the instrument100 to form a coil. The winds or turns of wire 110 are formed betweenguide posts 114 and can include a plurality of guide posts 114 that areformed or positioned at selected positions on the external wall 112 ofthe guide tube 100. There may be a plurality of turns of the wire 110between each guide post (e.g. FIG. 2) or there may be one turn of thewire 110 between each guide post (e.g. 144, FIG. 9). The wire can beinsulated so that it is insulated from the instrument 100 and the nextturn of the wire. It will also be understood that a portion includingthe coil of wire can be connected to the instrument to perform as thetracking device 52. For example, a sleeve with the coil of wire can befit over an outer wall of the instrument 100.

With additional reference to FIG. 3, the guide posts 114 can extend fromthe external wall 112 to a height above the external wall 112.Alternatively, the posts 114 can be understood to define a maximumdiameter of the instrument 100 and the wire 110 is wound, at leastinitially, within the maximum diameter. In other words, the wire 110 canbe maintained below the height of the posts 114 or can be wound over topof the posts 114. The posts 114, however, may provide the greatestdegree of guiding or support for the wire 110 when the wire 110 isbetween and below an outer edge of the posts 114.

The guide posts 114 are formed on the instrument 100 can include aslanted or guiding wall 116 and a support or second wall 118. Both theguide wall 116 and the support wall 118 can extend to an outer wall 117.The outer wall 117 can define an outer diameter or perimeter of theinstrument 100. The posts 114 can also define a width 114 w. The width114 w can be selected to engage the wire 110 in a manner to selectivelyhold the wire 110 or to cover a selected expanse of the instrument outerwall 112. Also, the posts 114 can be formed separately and adhered orfixed to the outer wall 112 (e.g. with adhesives, welding, threadedengagement) or can be formed as a single piece with the outer wall 112(e.g. molding or machining the posts 114 from the outer wall 112).

The guide wall 116 has a surface that can extend along a plane or line1161 that extends at an angle 116 a relative to a long axis 120 of theguide tube 100. The guide wall 116 can be the entire width 114 w of thepost or can be a selected portion thereof. It will also be understood,however, that the guide wall 116 need not be angled. For example, when afirst post 114 is formed on the instrument and a second post 114 isformed on the instrument the first and second post can be axiallypositioned relative to one another such that when the wire 110 is woundthe instrument 100 the wire 110 will achieve a selected angle to formthe navigation vector, as discussed herein.

It will be understood that the long axis 120 can be a long axis of anyappropriate instrument. Generally, the long axis 120 is substantiallyaligned with an end or length of the instrument 100 such that the longaxis 120 substantially defines a line or trajectory of the instrument100. Also, a second instrument may pass through the tube 100 theinstrument, such as a needle, generally along the long axis 120 andthrough an end of a guide tube 100. Thus, the long axis 120 generallydefines a long axis or real trajectory of an instrument or a portionbeing guided through a guide portion of an instrument relative to asubject. The long axis 120, however, may be any axis of the instrument100 and may only be aligned with a long axis of the instrument 100. Itwill be understood, however, that the instrument need not be rigidlystraight, but can be bent, curved, flexible, or otherwise moveable.Thus, the long axis 120 may refer to a long axis of a selected portionof the instrument 100 that may not be continuous for an entire length ofthe instrument 100.

The angle 116 a can be selected from any appropriate angle. Generally,however, the angle 116 a will be about 5 degrees to about 80 degrees,including about 10 degrees to about 80 degrees, and further includingabout 35 degrees to about 40 degrees relative to the long axis 120. Asdiscussed in U.S. patent application Ser. No. 12/770,181 filed on Apr.29, 2010 and published as U.S. Pat. App. Pub. No. 2010/0210939 on Aug.19, 2010, incorporated herein by reference, providing an angle between awrapped winding or coil of wire relative to the long axis 120 canprovide for forming a tracking device relative to the instrument 100that can determine an orientation or position of the instrument inmultiple degrees of freedom. It is understood, as disclosed herein,having multiple coils at various angles relative to one another canincrease the degrees of freedom tracking information (e.g. threedimensional position information and three degrees of orientationinformation, which can include yaw, pitch, and roll of the instrument).For example, one coil of wire can generally provide five degrees offreedom of location information (e.g. three position degrees and twoorientation degrees). An additional coil affixed to a single device(e.g. the instrument 100) can be used to solve for six degree of freedomlocation information including three position degrees and threeorientation degrees for a single instrument. Additional coils (e.g.three or more total coils) can be provided or used for redundancy andincreased information for location determination of the instrument.Generally, location is understood to include both position andorientation information.

As illustrated in FIG. 2, the coil winding 110 can include one ormultiple wires. The coil winding can also include a single wire that iswound multiple times around the instrument and to engage the angledsurface 116. Accordingly, a winding angle of the wire 110 can be definedalong the axis or a line 122 and generally defines an angle 122 a thatis similar to the angle 116 a defined by the guide wall 116 relative tothe long axis 120. The angle 122 a is achieved by contacting the wire110 against the guide wall 116 as the wire 110 is being wound around theinstrument 100. By contacting the guide wall 116, the wire 110 can beguided and maintained at the selected angle 122 a relative to the longaxis 120 of the instrument 100. It will be understood that if multiplewindings are used next to each of the posts 114 then each successivewinding may contact the previous wind of wire and not the angled wall116 directly, as illustrated in FIG. 4.

Also, as illustrated in FIG. 3, the posts 114 can be positioned aroundthe instrument 100, such as on opposed sides. However, it will beunderstood, that the posts 114 can be positioned at various offsetsaround the instrument 100. For example, the posts 114 can be positioned45 degrees from each other around the instrument 100 and displacedaxially for each successive post 114. Moreover, positioning the posts114 displaced axially along the instrument 100 can allow for achievingthe angle 122 a without the angled wall 116. As illustrated in FIG. 3,the wire 110 can be wound to contact an axially displaced post 114 toachieve the angle 122 a.

The angled wall 116 can also be provided to assist in the angle 122 acreation or initiation, as illustrated in FIG. 3. In addition, theangled wall can assist in creating clearance for winding of the wire110. For example, the angle between the top surface 117 and the wall 116reduces or eliminates a snag or catch point (e.g. the corner created bya right angle between the walls) for the wire 110. Also, the angled wallallows for tight winding of additional layers of wires laid on the firstor previous winding layer.

The selected angle 122 a, as discussed herein, allows for the generationof a navigation vector 124 that is at an angle 124 a relative to thelong axis 120 and complementary to the angle 122 a. The navigationvector 124 can generally be defined with the navigation system 10 bysensing a magnetic field with the tracking device 52 (e.g. having acurrent induced in the tracking device) defined by the plurality ofwindings 110 of wire or by emitting a field from the tracking device 52to be sensed by the localizer 42. In other words, the navigation vectoris defined in part by the position of the tracking device, but thevector is defined when used with the navigation system 10 by sensing themagnetic field or emitting a magnetic field. Regardless, the navigationvector 124 generally defines the angle 124 a relative to the long axis120 as disclosed in U.S. Pat. App. Pub. No. 2010/0210939.

With additional reference to FIG. 4, it will be understood that a singleor a plurality of windings can be provided on the instrument 100,according to various embodiments. For example, as illustrated in FIG. 4,according to various embodiments an instrument 100′ can include aplurality of guide posts 140 associated with the instrument 100′. Afirst number or a plurality of the guide posts 140′ can include or havea first angled wall 142 that directs or causes the windings of the wire110 to be formed relative to a long axis 120′ of the instrument 100along an axis 144 thus forming an angle 144 a relative to the long axis.The first angle or angle 144 a can be an acute angle relative to thelong axis 122′. Also, a plurality of windings, such as at least a secondwinding 110′, can be provided between each post 140′. A second portionor plurality of the guide post 140 can include the guide posts 140″ thathave a second guide wall 150 that will cause or form the wire 110 to bewrapped along an axis 152 relative to the long axis 120′ of theinstrument 100 and form an angle 152 a relative to the long axis 120′.The angle 152 a can generally be an angle different than the angle 144 aand can include a substantially 90 degree angle relative to the longaxis 120. Finally, a plurality of the guide posts 140 can include theposts 140″' and include a guide wall 156 that would cause the winding ofthe wire 110 to be formed along an axis 158 to form an angle 158 arelative to the long axis 120′. The fifth angle 158 a can generally bean angle different than the angle 144 a and the angle 152 a andgenerally, as illustrated, be an obtuse angle relative to the long axis120′. It will be understood that each of the different coils can be atsubstantially orthogonal angles relative to one another, but is notrequired. Also, as discussed above three coils is not required for sixdegree of freedom location information.

As illustrated in FIG. 4, a plurality of tracking device portions can beused to form the tracking device 52. The tracking device portions caninclude windings of the wire 110 that are formed at a plurality ofangles, such as three angles, relative to the long axis 120′ of theinstrument 100′. Each of the different windings that are at differentangles relative to the long axis 120′ can be substantially separated orinsulted from one another to allow for the generation of three discreetsignals. This can allow for the determination of three discreetnavigational axis relative to the instrument 100′ as disclosed in U.S.Pat. App. Pub. No. 2010/0210939. In allowing for the generation of threediscreet signals, three discreet navigational axes are determined foreach of the different angles of the windings relative to the long axis120′ of the instrument 100′. This can allow for the determination of aplurality of degrees of freedom due to tracking the three discreetangles or three discreet portions at a different orientations relativeto the long axis 120′ of the instrument 100′. It will be understood thatany appropriate number of discreet angle portions can be made relativeto the instrument 100′ and three is merely exemplarily.

In addition or alternatively to having the wire wrapped to form aplurality, such as three angles, as illustrated in FIG. 4, a pluralityof different angles can be formed by rotating the navigation vectorsrelative to the long axis 120″, as illustrated in FIG. 5A. The long axis120″ is defined by an instrument 100″, which can be the same ordifferent than the instruments discussed above. The instrument 100″ caninclude one or more guide posts 140 a, 140 b, and 140 c spaced apartaxially along the length of the instrument 100″. Additionally, each ofthe guide posts is rotated around the long axis 120″ of the instrument,as further illustrated in FIG. 5B. Angles between each the guide posts140 a, 140 b, 140 c can be an appropriate angle, such as about 90-150degrees, including about 100 degrees to about 150 degrees, and furtherincluding about 120 degrees (as exemplary illustrated by at least oneangle RA₁, RA₂, RA₃).

With reference to FIGS. 5A and 5B, the instrument 100″, can include atleast three tracking devices or portions 110 a, 110 b, and 110 c. Eachof the tracking devices 110 a, 110 b, and 110 c positioned on theinstrument 100″ can include or define a navigation vector 160 a, 160 b,and 160 c. Therefore, the first navigation vector 160 a can be formed bya first tracking device 110 a, the second navigation vector 160 b can beformed by the second tracking device 110 b, and the third navigationvector 160 c can be formed by the third tracking device 110 c relativeto the instrument 100″. Each of the navigation vectors 160 a, 160 b, and160 c can be formed relative to the instrument 100″ due to thepositioning of the windings of material of the respective trackingdevices 110 a, 110 b, and 110 c at the winding angle relative to theinstrument 100″.

FIG. 5B attempts to illustrate on a two-dimensional plane of a page athree-dimensional rotation of angles of the three different windings ofthe wire 110 a, 110 b, and 110 c. As discussed above, in relation toFIG. 4, each of the windings can be wound at the winding angle relativeto the long axis 120′ of the instrument 100′. As illustrated in FIGS. 5Aand 5B, however, rather than having the windings formed at various anddifferent winding angles relative to the long axis 120″ of theinstrument 100″, each of the windings 110 a, 110 b, and 110 c can beformed at substantially a single winding angle, including those windingangles discussed above and such as about 20 degrees to about 70 degrees,relative to the long axis 120″ of the instrument 100″.

Because each of the coils of the tracking device windings 110 a, 110 b,and 110 c are at the same winding angle, to resolve the six degrees offreedom of location a top or high point Ha, Hb, Hc of each of the coilwindings 110 a, 110 b, and 110 c are rotated rotation angles RA₁, RA₂,and RA₃, such as about 120 degrees relative to one another, around thelong axis 120″ of the instrument 100″. As discussed above, however,three windings are not required and an appropriate number of windings(e.g. only two windings 140 a and 140 b) can be used with an appropriatenumber of localizer coils. The rotation angles RA1, RA2, and RA3, can beselected to be 120 degrees to place each of the tops Ha, Hb, Hcsubstantially equidistant apart around the long and central axis 120″ ofthe instrument 100″. It will be understood, however, that the rotationangles RA₁, RA₂, and RA₃ can be about 90 degrees to about 180 degrees,including about 120 degrees. The at different rotation angles a distanceabout the long axis 120″ between each of the vectors 160 a-160 c and/orthe posts 140 a-140 c will also vary.

As illustrated in FIG. 5B, the front or top end of the windings Ha-Hcare all in substantially the same direction, such as towards a distalend of the instrument 100″. Each of the windings 110 a-110 c are, thus,rotationally spaced apart around the center long axis 120″ of theinstrument 100″. In this way, the navigation vectors 160 a-160 c foreach of the windings 110 a-110 c can be formed at the same winding anglerelative to the long axis 120″ of the instrument 100″. The navigationvectors 160 a-160 c are also, due to the rotational spacing of the coilwindings tops Ha-Hc, rotationally spaced around the long axis 120″.

The different navigation vectors 160 a-160 c are defined relative to acenter 101 of the instrument 100″. Each of the vectors 160 a-160 c canpoint towards a plane P, as illustrated in FIG. 5A, which is the planeof the page in FIG. 5B. The tails of the vectors 160 a-160 c can go intoand past the plane on the page, thus all of the navigation vectors 160a-160 c are not coplanar, but they all intersect the single plane P.Each of the vectors 160 a-160 c can be formed relative to the plane Protationally spaced at the rotation angles relative to one anotheraround the center 101 of the instrument 100″.

As discussed above, the navigation vector angle can be selected byforming the windings of the tracking device 110 a-110 c at a selectedangle relative to the long axis of the coil winding 110 a-110 c whichcan also be the long axis of the instrument 120″. By changing thepositioning of the angle of the rotation of the windings of the varioustracking devices, the navigation vectors can be positioned relative tothe instrument 100″ in this selected manner. In various embodiments, thevectors 160 a-160 c are differently oriented relative to the instrument100″ by having more than one coil wound at the same winding angle, butbeing spaced relative to one another with the rotation angles.

The guide posts 140 a-140 c can be similar to those discussed above, butspaced axially along the axis 120″ of the instrument 100″. Thus, each ofthe guide posts can include top walls 117 a-117 c and angled walls orguide walls 156 a-156 c. Each of the angled walls can have the sameangle as each of the coils 110 a-110 c can have the same angle. However,the guide posts 140 a-140 c positioned at varying rotational positionsaround the long axis 120″ allows for the formation of differentnavigation vectors 160 a-160 c relative to the long axis 120″ of theinstrument 100″.

Also, each of the coil portions 110 a, 110 b, 110 c can be formed onseparate members and interconnected for a use. For example, each of thecoils could be formed on separated hollow members are that can be placedover the instrument 100″ or over another hollow member. Each of themember can include an index finger and an index groove to ensure thatthe respective navigation vectors 160 a-160 c would be defined at theselected angle relative to one another. Thus, each of the coils 110 a,110 b, and 110 c need not be formed on the same or rigid member.

With reference to FIG. 6, the instrument, according to variousembodiments is illustrated as an instrument 200. Instrument 200 canextend along a long axis 202 and define an internal cannula or bore 203.Accordingly, the instrument 200 can include an external wall 204 whichcan be inserted into a subject, such as the patient 14. The instrument200 can be a guide tube or other guide instrument through which a secondinstrument, such as a drill bit or needle, is passed and guided.Alternatively, or in addition thereto, it will be understood that theinstrument 200 may be solid, hollow, or cannulated and exemplarily be adrill bit, a probe, or other appropriate instrument. Accordingly, theexemplarily instrument 200 is merely for illustration for the currentdiscussion.

The instrument 200 can include the tracking device 52 associated withthe instrument 200. The tracking device 52 can include various portionsthat are operable in the navigation system 10 to allow for thedetermination of a location (including position and orientation) of theinstrument 200. Generally, location information can include X, Y and/orZ dimensional coordinates along with at least two orientationcoordinates (and when 6 degrees of freedom are determined at least threeorientation coordinates). As discussed above, two separate coils can beused to solve for six degrees of freedom location information.

The tracking device 52 can be selected to include three sets of coils,although more or fewer coils can be selected based on the amount oflocation information selected. Each set of coils or coil can include aplurality of windings of a wire that can generate or be used todetermine a navigation vector separate from the other coils or windingsof wire. Accordingly, the navigation or tracking device 52 can include afirst coil of wire 206 wound around a surface of the outer wall 204 orembedded in the surface of the outer wall 204 of the instrument 200. Thewire of the coil 206 is generally insulated both from adjacent turns ofthe wire and from the instrument 200. Generally, the first coil 206 iswound around the long axis 202 and substantially coaxial therewith.Accordingly, the first coil 206 can define a navigation vector thatgenerally aligned with the long axis 202 of the instrument 200. It willbe understood, however, that the first winding need not be coaxial withthe long axis 202.

A second coil set can include coil portions 208 a and 208 b. The coilportions 208 a, b generally includes two coils that can be formed of awire wound in a selected shape, such as an oval, circle, or ellipses,around a winding axis. The wire can be generally flat wire or a wirethat has a round cross-section. As illustrated, the wire is wound in anoval having a long or major radius 210 generally along or aligned withthe long axis 202 of the instrument 200, wherein the major radius 210extends from a focus of the respective coil portion 208 a,b to an edgeof the respective coil portion 208 a,b. The coil portion 208 a also hasa short or minor radius 212 generally perpendicular from the long radius210 of the respective coil portions 208 a or 208 b, wherein the minorradius 212 also extends from the focus of the respective coil portion208 a,b towards an edge thereof. The coil portions 208 a and 208 b canbe connected in series and positioned about 180 degrees from one anotheraround the surface of the outer wall 204 of the instrument 200 andaround the long axis 202.

Again, the coil portions 208 a and 208 b are generally positioned on theouter wall 204 or positioned at or in a holding region, for example in adepression in the outer wall 204 of the instrument 200. The depressioncan hold the coil portions 208 a, 208 b alone (e.g. with an interferencefit) and/or they can be adhered within the depression. For example, thedepressions can be filled with a selected epoxy or adhesive to hold thecoil portions 208 a, b in place.

Accordingly, both of the coil portions 208 a and 208 b work as a singlecoil to increase the electromagnetic (EM) signal from the respectivecoil portions 208 a and 208 b. It will be understood, as discussedabove, that the coil portions 208 a and 208 b can either receive ortransmit an electromagnetic field to generate the EM signal.Additionally, the coil portions 208 a and 208 b can be wound around acore. The core can includes an EM permeable core material or be formedaround an air core, as selected, for signal strength. Further, the coilportions 208 a,b can be formed of a plurality of turns of insulatedwire.

A third coil 220 can be formed as a first coil portion 220 a and asecond coil portion 220 b (not illustrated) positioned substantially 180degrees from the first coil portion 220 a around the long axis 202 ofthe instrument 200. Again, each of the coil portions 220 a and 220 b canbe formed by winding a wire in a selected shape around a winding axis,such as an oval including a long radius 222 generally aligned with thelong axis 202 of the instrument 200 and a short radius 224 that isgenerally perpendicular to the long radius 222 of the coil portion 220a. Further, each of the coil portions 220 a and 220 b can be positionedon a surface or in a depression formed in the surface of the outer wall204 of the instrument 200. Further, the two coil portions 220 a and 220b can be connected in series similar to the coil portions 208 a and 208b to increase the EM signal or sensitivity and reduce relative size pertotal number of windings relative to the instrument 200. Further, thecoil portions 220 a,b can be formed of a plurality of turns of insulatedwire.

Each of the coil portions 208 a, 208 b, 220 a, and 220 b can bepositioned at a selected angle 234 from one another around the long axis202 of the instrument 200. As illustrated in FIG. 6, the angle 224 canbe a 90 degree angle formed between the coil portions 208 a, 208 b, 220a, and 220 b and is defined as an angle 234 formed by two lines 230 and232 that intersect at the long axis 202 of the instrument 200 and extendthrough the centers of two adjacent of the coil portions, such as 208 aand 220 a. The lines 230 and 232 can also be defined as extendingperpendicular from a plan defined by an outside of the respective coilportions 202 a,b and 220 a,b that intersects the axis 202. The 90 degreeangle is an angle 234 formed between the two lines 230 and 232.Accordingly, each of the coil portions 208 a, b and 220 a, b can bepositioned around the long axis 202 of the instrument 200.

Further, the navigational vectors of the respective coil portions 208and 220 will generally be along the respective lines 230 and 232.Accordingly, these two navigational vectors are generally 90 degreesrelative to one another and are at different angles relative to thenavigational vector that would generally be along the long axis 202formed by the first coil 206 and near the first coil 206. It will beunderstood, however, that the navigation vectors from the coil portions208 and 220 can be positioned relative to the instrument 200 by changingthe angle 224 to be a angular offset of the respective coil segments(e.g. more or less than 90 degrees) and by angling the surface of thewindings of the respective coil portions 208 and 220 relative to thelong axis 202 of the instrument 200.

In one example, the coil portions 208 and 220 can have an end nearer thedistal end 240 positioned a distance further from the axis 202 than anend further from the distal end 240, as exemplarily illustrated inphantom coil 208 a′. Although, the coil portions 208 and 220 can beangled in any appropriate manner to generate a selected navigationvector relative to the instrument 200. Accordingly, the line 230 can beformed to be substantially not perpendicular to the long axis 202 of theinstrument 200 to change the navigational vector of the coil portions208. By altering the navigational vector in such a manner, therespective navigation vectors can be used to identify differentpositions of the respective coil segments relative to the instrument 200for different or increased navigational accuracy.

Moreover, it will be understood that a greater number of coil portionscan be positioned on the instrument 200. For example, additional ovalcoil portions can be positioned at different angles relative to theinstrument 200, such as about 45 degrees relative to the illustratedcoil portions, at a position further from the distal end 240. Theseadditional coil portions can generate additional navigational vectorsrelative to the instrument 200 for increased navigational accuracy. Theadditional coil portions can be used for backup, error detection,location verification, and other appropriate reasons. All of the coilsets can act independently for navigation vector determination. Also, itwill be understood, that the coil portions need not be at 90 degreesrelative to one another.

With reference to FIGS. 7 and 8, an instrument 300 according to variousembodiments is illustrated. The instrument 300 can be similar to theinstruments discussed above, such as a stylet, a guide tube, a drillbit, or other appropriate instrument to be moved relative to a subject,such as the patient 14. The instrument 300 can include the trackingdevice 52 which includes a plurality of tracking elements 302, 304, and306. Each of the respective tracking elements 302, 304, and 306, can bepositioned along a long axis 308 of the instrument 300. It will beunderstood, as discussed above, that more or less than three trackingelements can be provided with the instrument 300.

According to various embodiments, the tracking elements 302, 304, and306 can be embedded or positioned within a holding portion, such as oneor more recesses 310 formed in the instrument 300. The elements 302, 304and 306 can be positioned in the recesses 310 such as by molding,machining the recess 310 and affixing the navigation portions within therecess 310, or any other appropriate configuration. The shape of thetracking elements 302, 304, and 306, as discussed herein, can includeflat or planar portions that can be keyed or fit with an interferencefit with the holding portion or each of the recesses 310. In addition,or alternatively to the keyed fit, the tracking elements 302, 304, and306 can be affixed within the recesses 310 with an adhesive, such as anepoxy, to fix the tracking elements 302, 304, and 306 relative to theinstrument 300.

Each of the three tracking elements 302, 304, and 306 can be formed orprovided as a coil of wire wrapped around a selected core 312. The core312 can be a highly magnetically permeable core or an air core to formeach of the respective tracking elements 302-306. Generally, each of thetracking elements, such as the tracking element 302 illustrated in FIG.8, is wrapped around the core 312 and will define a navigation vector oraxis 314 that is generally aligned with an axis about which the trackingelements 302 or, the respective other tracking elements, is wrapped.

Generally the tracking element 302, or any other appropriate trackingelements, are barrel-wrapped around the core 312 such that the coil iswide near a central portion 316 and tapered towards the respective ends318 and 320 of the respective tracking elements 302-306. The endsurfaces at the respective ends 318 and 320 can generally be flat to bekeyed or have an interference fit within the holding portion recesses310. Also, the shape of the windings of the tracking elements 302-306can generally be defined by the core 312, especially if the core 312 isa shaped material. Thus, the winding is generally around the navigationaxis 314.

As specifically illustrated in FIG. 8, the coil winding wraps around thecore 312 of the tracking element 302 to be small on the first end 318wider in the center 316 and taper again to a smaller end 320.Accordingly the tracking element 302 can generally or roughly define abarrel shape to be positioned within or on the instrument 300 in aselected or indexed manner. The barrel shape generally has flatter orflattened ends so that its orientation is maintained and can be selectedrelative to the instrument 300. It will be understood that a core can beselected to include the barrel shape of the winding of the wire can formthe barrel shape. It is also understood that a barrel shape is notnecessary and other shapes can be selected. Also, a core shape can beselected to index or be fit fixedly within the recesses 310.

The appropriate plurality of navigation vectors can provide theinstrument 300 with a six degree of freedom tracking device 52 as eachof the coil elements can be positioned such that their respectivenavigation vectors 314, 330, and 332, are positioned substantiallyorthogonal relative to one another along the longitudinal length of thelong axis 302 of the instrument 300. Although, it is understood thatthree different vectors are not required to obtain the six degree offreedom information, as discussed above. By providing the plurality ofnavigational vectors or axes of winding of the tracking elements 302-306(e.g. indexing or fixing the tracking elements 302-306 at differentangles relative to the instrument 300), a plurality of vectors can beidentified for the instrument 300 using each of the individual trackingelements 302-306. Accordingly, the instrument 300 can be navigated withsubstantially six degrees of freedom of location information determininglocation information of each of the respective tracking elements302-306. However, each of the coil elements need not be overlapping oneanother and can be positioned at any appropriate location within theinstrument 300.

Additionally, it will be understood, that each of the tracking elements302-306 can be positioned at any appropriate location relative to theinstrument 300 or any other appropriate instrument. Accordingly, havingthe plurality of tracking elements 302-306 as substantially next to oneanother, as illustrated in FIG. 7, is not required and they can bespaced apart for various reasons. For example, communication lines, suchas to an ablation electrode, may pass between the respective trackingelements 302-306 and the spacing may be altered for such considerations.However, knowing the location of the respective tracking elements302-306 relative to each other and the instrument 300 allows fornavigation of the instrument 300 with substantially six degrees offreedom with the navigation system 10.

It will be understood that various instruments, especially theinstruments 100, 200, and 300, are illustrated herein for examples.However, a plurality of instruments can include all or individually thevarious tracking devices or portions thereof illustrated in particularembodiments. For example, as illustrated in FIG. 9, an instrument 400,according to various embodiments, can include one or more of each of theselected portions of the tracking device 52. Accordingly, the trackingdevice 52 can include oval coil segments 208 a and 208 b connected inseries on the instrument 400. Additionally, an angled coil, such as thecoil configuration 144 can be provided between guide posts 140′ on theinstrument 400. Additionally, a coil element, such as the coil element308 can be provided within the instrument 400. Each of the respectivecoil elements can include navigation vectors that are positioned atdifferent angles relative to one another, such as substantiallyorthogonally or otherwise non-aligned. For example, the coil elements208 a, b can define a navigation vector 402 that can be perpendicular toa long axis 406 of the instrument 400. The coil winding 144 can define anavigation vector 408 at a selected angle relative to the long axis 406.Finally, the coil element 308 can define a third navigation vector 410relative to the long axis 406 that can also be generally perpendicular,but in the opposite or different direction of the coil elements 208 a,208 b or aligned with the long axis. Accordingly, each of the three coilportions or segments can be positioned on the instrument 400 where eachhave different configurations, as discussed above, while providing aplurality of navigation vectors relative to the instrument 400.Accordingly, it will be understood that the instrument 400, according tovarious embodiments, need not include a substantially consistent coilsegment design and can be provided for different coil segmentconfigurations.

It will be understood that the tracking device 52 can be positioned onan instrument that is substantially not rigid. For example, theinstrument can be movable or bendable and have portions that rotaterelative to other portions of the instrument. Also, the tracking device52 can be positioned on a probe that can be angled and rotated relativeto the patient 14, or any appropriate subject. Accordingly, therotational direction and orientation relative to the subject along withits three-dimensional position can be determined. Additionally, thetracking device 52 can be positioned on a substantially continuouslyrotating instrument, such as a drill bit, to be moved relative to thesubject, such as the patient 14, and the location and other position andorientation information can be determined in the navigation system 10.Accordingly, providing the tracking device 52 and a guide tube or probeor substantially slow-moving instrument is not required, and thetracking device 52 can be placed on any appropriate instrument fornavigation in the navigation system 10. For example, the elements of thetracking device 52 can be assembled and the tracking device assembly canbe attached to a handle of the instrument 100, 200, 300 and 400.

The tracking devices, according to any embodiments discussed above, canbe provided directly on instruments as illustrated above. It will beunderstood, however, that the tracking devices can be provided on otherportions or members that can be interconnected or attached to anyappropriate instrument. For example, as illustrated in FIG. 1, thetracking device 52 can be connected with a stem or pedestal toinstrument to track the instrument. Accordingly the tracking device canbe positioned on an instrument that is not originally formed withinstrument so that the instrument can include the tracking device.

Additionally, the tracking devices can be provided to minimize ormaintain an outer diameter or perimeter of the instrument. Although thecross section of the instrument can be provided in any selected shape(e.g. round, square, oval), the tracking devices can be provided tominimize an increase in an outer perimeter dimension, such as adiameter, due to the positioning of a tracking device on the instrument.For example, the tracking device including the coil 110, as illustratedin FIG. 2 with the instrument 100, can be wrapped around the instrumentto be substantially maintained within an outer diameter of theinstrument 100. As illustrated in FIG. 6, coil portions 208 and 220 canbe positioned within depressions in the instrument 200 to assist insubstantially maintaining an outer diameter of the instrument 200. Inaddition, these coil segments 208 and 220 can be made relatively flat(e.g. having a height of less than about 1 mm, including about 0.1 mm toabout 1.0 mm) relative to the instrument 200 to assist in maintaining anouter diameter of the instrument 200 after positioning the coil segmentsrelative to the instrument 200. Further, the tracking device portions302, 304, and 306 illustrated in FIGS. 6 and 7 can be positioned on theinstrument 300 substantially within an outer diameter of the instrument300. In particular, the tracking portions can be embedded within anouter diameter of instrument 300 to maintain the size of the instrument300 for various purposes. Accordingly, the tracking devices, accordingto the various embodiments, can be connected with instruments to assistin maintaining a dimension of the instrument for purposes of assistingin minimizing the size of instrument for surgical procedures. It will bealso understood that the tracking devices can interconnected with otherinstruments to assist in tracking instruments for nonsurgicalprocedures, such as manufacturing, exploration, and other purposes.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

1. A navigation system, comprising: an instrument that is operable to bemoved relative to a subject and having an exterior wall that defines aninstrument axis; a holding portion defined by the instrumentsubstantially within a surface of the exterior wall; and a trackingdevice formed of at least a first conductive wire wound in a first ovalhaving a first minor radius and a first major radius and connected inseries to at least a second conductive wire wound in a second ovalhaving a second minor radius and a second major radius; wherein thefirst conductive wire and the second conductive wire are angularlyoffset around the instrument axis of the instrument and positioned inthe holding portion of the instrument; wherein the first conductive wireand the second conductive wire both define a first navigation vector andhave a combined higher electromagnetic signal than either of the firstconductive wire and the second conductive wire alone.
 2. The navigationsystem of claim 1, wherein the tracking device further comprises: athird conductive wire wound in a third oval and a fourth conductive wirewound in a fourth oval; wherein a line that intersects the instrumentaxis of the instrument and is perpendicular to a first plane of thefirst conductive wire forms an angle relative to any other line that isperpendicular to a second plane of the second conductive wire, a thirdplane of the third conductive wire, or a fourth plane of the foursconductive wire.
 3. The navigation system of claim 2, wherein the firstconductive wire and the second conductive wire are substantially180-degrees from one another around the instrument and the fourthconductive and third conductive wire are substantially 180-degrees fromeach other around the instrument.
 4. The navigation of claim 3, whereinthe first conductive wire and the second conductive wire define thefirst navigation vector and the third conductive wire and the fourthconductive wire define a second navigation vector; wherein the firstnavigation vector and the second navigation vector are formed at anglesrelative to one another.
 5. The navigation system of claim 4, furthercomprising: a fifth conductive wire wrapped around the instrument andwound around an axis that is substantially aligned with the axis of theinstrument; wherein the fifth conductive wire defines a third navigationvector that is at an angle to both the first navigation vector and thesecond navigation vector.
 6. The navigation system of claim 5, furthercomprising: a localizer operable to generate an electromagnetic field;wherein the first conductive wire and the second conductive wire sensethe electromagnetic field and generate a signal regarding the firstnavigation vector, wherein the third conductive wire and the fourthconductive wire sense the navigational field and generates a signalbased upon the second navigation vector, and the fifth conductive wiresenses the electromagnetic field and generates a third signal based uponthe third navigation vector.
 7. The navigation system of claim 4,wherein all of the first conductive wire, the second conductive wire,the third conductive wire, and the fourth conductive wire each wound inthe respective first oval, second oval, third oval, and fourth oval eachinclude a thickness less than the exterior wall of the instrument suchthat an exterior dimension of the instrument is not substantiallyincreased.
 8. The navigation system of claim 1, wherein at least two ofthe first conductive wire, the second conductive wire, the thirdconductive wire, or the fourth conductive wire are axially displacedfrom one another.
 9. A navigation system, comprising: an instrument thatis operable to be moved relative to a subject and having an exteriorwall that defines an instrument axis; a holding portion defined by theinstrument substantially within a surface of the exterior wall; and atracking device having: a first conductive wire wound around a firstwinding axis and connected in series to at least a second conductivewire wound around a second winding axis; a third conductive wire woundaround a third winding axis and connected in series to at least a fourthconductive wire wound around a fourth winding axis; wherein the firstconductive wire and the second conductive wire are at least one ofangularly or axially offset from one another and the third conductivewire and the fourth conductive wire are at least one of axially orangularly offset from one another around the instrument axis of theinstrument and all of the first conductive wire, the second conductivewire, the third conductive wire, and the fourth conductive wire arepositioned in the holding portion of the instrument; a localizeroperable with the tracking device to generate signals regarding positionand orientation information of the instrument; and a navigationprocessor operable to execute instructions to determine a plurality ofdegrees of freedom location information regarding the instrument basedon the generated signals regarding position and orientation informationof the instrument from the tracking device.
 10. The navigation system ofclaim 9, wherein each of the first conductive wire, the secondconductive wire, the third conductive wire, and the fourth conductivewire are wound around the respective winding axes generally in the shapeof an oval such that each of the first conductive wire, the secondconductive wire, the third conductive wire, and the fourth conductivewire windings having a major radius generally aligned with theinstrument axis of the instrument.
 11. The navigation system of claim10, wherein each major radius is angled relative to the instrument axisof the instrument.
 12. The navigation system of claim 10, wherein thefirst conductive wire includes a plurality of turns of the firstconductive wire around the first winding axis, the second conductivewire includes a plurality of turns around the second winding axis, thethird conductive wire includes a plurality of turns around the thirdwinding axis, and the fourth conductive wire includes a plurality ofturns around the fourth winding axis.
 13. The navigation system of claim12, wherein the first conductive wire and the second conductive wire areconnected in a series and positioned substantially 180-degrees from oneanother around the instrument axis of the instrument.
 14. The method andnavigation system of claim 13, wherein the third conductive wire and thefourth conductive are connected in series to one another in positionsubstantially 180-degrees from one another around the axis of theinstrument.
 15. The navigation system of claim 14, further comprising: aholding portion mount; wherein the first conductive wire, the secondconductive wire, the third conductive wire, and the fourth conductivewire are each adhered in the holding portion; wherein the holdingportion is affixed to the instrument with the holding portion mount. 16.The navigation system of 9, further comprising: a fifth conductive wirewound around a winding axis such that the winding axis of the fifthconductive wire is generally aligned with the axis of the instrument.17. A method of making an instrument for navigation relative to asubject, comprising: providing an instrument that is operable to bemoved relative to a subject and having an exterior wall that defines aninstrument axis; forming a holding portion defined by the instrumentsubstantially within a surface of the exterior wall; and forming atracking device by: winding a first conductive wire around a firstwinding axis to form a first winding; winding a second conductive wirearound a second winding axis to form a second winding; connecting inseries the first winding and the second winding; winding a thirdconductive wire around a third winding axis to form a third winding,winding a fourth conductive wire around a fourth winding axis to form afourth winding; connecting in series the third winding and the fourthwinding; wherein a line perpendicular to the instrument axis of theinstrument and through each one of the first winding, the secondwinding, the third winding, and the fourth winding is angularly offsetare from each other of the perpendicular lines.
 18. The method of claim17, further comprising: forming the angular offset at aboutninety-degrees.
 19. The method of claim 17, further comprising: windinga fifth conductive wire around a fifth winding axis such that the fifthwinding axis of the fifth conductive wire is generally aligned with theinstrument axis of the instrument.
 20. The method of claim 17, furthercomprising: producing signals with the tracking device regardingposition and orientation information of the instrument; and executinginstructions with a navigation processor to determine at least sixdegrees of freedom location information regarding the instrument basedon the produced signals regarding position and orientation informationof the instrument from the tracking device.
 21. The method of claim 20,further comprising: moving the instrument relative to the subject;receiving the signals with the navigation processor from the trackingdevice as the instrument is moved relative to the subject; anddisplaying a representation of the determined location of the instrumentrelative to the subject.
 22. The method of claim 17, further comprising:providing the first winding and the second winding axially offset fromone another along the instrument axis.